Squall would be my first choice as I friggin' love the gunblade. I'm insanely jealous of Jiro who has a replica one. Can you I have it, Dak? Please?

I'd also have Quistis in my party whenever she's available. The rest are interchangeable. I'd probably use Selphie the least as I didn't really like her character. I really don't mind Zell even though it seems everyone else would rather eat their own hands than be forced to use him.

I generally pick them based on whether I like them more than their ability. Though while Squall isn't my favourite main character, his gunblade is just too awesome to ignore.